1. Field of the Invention
The present invention relates to a spool valve for controlling fluid flow, and particularly to a valve which is readily convertible to provide a variety of fluid flow modes.
2. Description of the Prior Art
Although the present invention has utility in connection with other fluid handling applications, it has particular relevance to water softeners having tanks containing material through which hard water is passed for softening. It is often desirable to bypass the tank, such as when the softener must be repaired or when the user will be absent for an extended period of time. The bypass valve used to do this is also commonly used in non-automatic types of water softeners to enable periodic replacement of the tank with one having a fresh charge of softener material.
It is desirable in many instances to provide a backwash function in addition to the service and bypass functions of a typical bypass valve. During backwashing, water is directed through the water softener equipment in a reverse direction to agitate, flush out, or carry off impurities and other foreign materials which have collected in the system. Generally these impurities will have collected at or near the top of the conditioner tank as a result of normal water flow direction and as a result of the normal softening or filtering process. A suitable backwash valve provides a path for the trapped impurities to be flushed down a drain.
My U.S. Pat. No. 4,250,920 entitled "Valve for Water Treatment Equipment", and issued Feb. 17, 1981, discloses a valve operative to perform the service, bypass and backwash functions just described. Althrough the valve generally operates satisfactorily, there are a number of areas in which improvements are desirable. For example, the valve is complicated by the provision of a rotatable bonnet to achieve the backwash function. In addition, the valve employs a fixed or integral post to threadably receive a one-piece valve stem. Such a threaded post involves extra production cost, and the one-piece nature of the valve stem necessarily requires a longer and somewhat larger valve body. Also, this design requires that at least one of the sealing spools be rotatable on the shaft and be sealed around the shaft. This complicates manufacture and valve assembly and disassembly. Also, maintenance or repair of the valve requires complete removal of the valve stem in order to replace the spools or associated seats. Several features of the design also raise the cost of production. Further, ease of movement of the bonnet into and out of the backwash position varies as the internal valve pressure varies. As pressure increases the bonnet becomes more difficult to move. Finally, the sequence of operation began from a service mode, then to a bypass mode and finally to a backwash mode. However, the sequence usually desired is between service and backwash modes, with only an occasionaal movement of the valve to the bypass mode. In some instances only service and backwash modes are of interest.